Résumé de la thèse en Anglais

In recent years, the interest of the scientific community has shifted increasingly towards the production and use of biochar in agriculture as an amendment. In addition to being an efficient means of recovering agricultural and forestry waste, it could contribute to restoring the fertility of tropical oxisols and thus maintaining the productivity of tropical agricultural ecosystems. As a result, this restoration could help in decreasing the pressure on rainforests, that is, deforestation for agricultural production. This field study was carried out in the West region of Cameroon in Central Africa. Its aim was to produce, characterize and test the effect of two biochars from agricultural and forestry origin on the physico-chemical properties of an oxisol and on maize production and maize nutritional equilibrium. Firstly, we constructed locally a retort kiln that improves on the currently-used technology (gas recycling, smoke and pollution reduction, higher biochar yield). The two biochars made from local residues (eucalyptus bark and corn cobs) using this improved kiln at 300 ° C, were characterized using ASTM, IBI and EBC methods. The field experiment included 30 irrigated plots of 4 m × 4 m each, in a split plot design. Two soil tillage modes: flat plowing and furrow-ridges, with three replicates were compared with four biochar treatments, incorporated to soil at the beginning of the first production period. The basic treatment in all plots was the recommended mineral fertilizer rate for maize production in the area: 200 kg NPK +100 kg N. Biochar was applied at 15 t ha-1. Maize yield, soil physico-chemical properties and leaf nutritional equilibrium were assessed, six and twelve months after application of the biochar. The results were analyzed using SAS GLIMIX procedure followed by the Tukey HSD multiple comparison test when necessary.
Results suggest the following conclusions: Eucalyptus bark and corncob biochars fulfill most of the criteria definition proposed by IBI and EBC for biochars. According to IBI, these are class 3 biochars (10 ≤ Corg ≤ 30). The new pyrolyser can thus be used to produce good quality biochar from common residues in Cameroon with reduced gas emissions. The application of biochar under our conditions has had little effect on the physicochemical properties of the soil; however, the significant increase in pH (0.3 and 0.5 units) and soil organic carbon (0.4 %) makes this technology acceptable for the global program "4 per 1000" initiated by France after Cop 21. Foliar nutritional analysis revealed a significant increase in the Mg and Ca content of maize plants in biochar amended plots; the yield per hectare of maize increased by 54 % during the first production period and by 51 % during the second in the biochar amended plots compared to the control. This increase in yield is otherwise translated into 25 % avoided deforestation due to agriculture. All these results indicate that biochar could be a valuable tool to face the challenges of deforestation and climate change in the humid tropical zones, through sustainable agricultural production.